Prevention of Sacituzumab Govitecan-related Neutropenia in Patients With Metastatic Triple Negative Breast Cancer

Inclusion Criteria:

1. Signed Informed Consent Form (ICF) prior to participation in any study-relatedactivities.

2. Patients aged ≥19 years at the time of signing ICF.

3. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

4. Life expectancy of ≥ 12 weeks.

5. Histologically confirmed TNBC per American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) criteria based on local testing on themost recent analyzed biopsy. Triple-negative is defined as <1% expression forestrogen receptor (ER) and progesterone receptor (PgR) and negative for humanepidermal growth factor receptor 2 (HER2) (0-1+ by IHC or 2+ and negative by in situhybridization [ISH) test].

6. Metastatic disease documented by computerized tomography (CT) scan or magneticresonance imaging (MRI) that is not amenable to resection with curative intent.

7. Refractory to at least one, and no more than two, prior standard of carechemotherapy regimens for unresectable locally advanced or MBC. PARP inhibitor couldhave been counted as prior chemotherapy for purposes of study eligibility.

8. All patients must have been previously treated with taxanes regardless of diseasestage (adjuvant, neoadjuvant, or advanced), unless contraindicated for a givenpatient.

9. Measurable or non-measurable, but evaluable disease, as per RECIST v.1.1. Patientswith bone-only metastases are also eligible.

10. Brain MRI must be done for patients with suspicion of brain metastases and patientmust have stable central nervous system (CNS) disease for at least 4 weeks afterlocal therapy, without neurological symptoms, and off anticonvulsants and steroids (no more than 10mg/day prednisone or its equivalent) for at least 2 weeks beforefirst dose of study treatment.

11. Meet the following organ function requirements:

• Hemoglobin ≥ 9 g/dL

• ANC ≥ 1500/mm3

• Platelets ≥ 100,000/μL

• Bilirubin ≤ 1.5 X IULN or ≤ 3X IULN for patients with documented Gilbert'ssyndrome

• AST and ALT ≤ 2.5 X IULN or ≤ 5 X IULN if known liver metastases

• Serum albumin > 3 g/dL

• Creatinine clearance ≥ 60 mL/min or ≥ 30 mL/min as assessed by theCockcroft-Gault equation

• INR/PT and PTT or aPTT ≤ 1.5 X IULN unless patient is currently receivingtherapeutic anticoagulant therapy

12. Resolution of all acute AEs of prior anti-cancer therapy to grade 1 as determined bythe NCI-CTCAE v.5.0 (except for alopecia or other toxicities not considered a safetyrisk for the patient at investigator discretion).

13. Male patients and female patients of childbearing potential who engage inheterosexual intercourse must agree to use institution specified method(s) ofcontraception during treatment with sacituzumab govitecan and for 6months after thelast dose.

• Required contraception for female of childbearing potential patients usinghormonally based method, intrauterine device (IUD), bilateral tubal occlusion,female condom with spermicide should during study period and continue until 6months after the last dose of latest administered study drug

• Required contraception for male patients using abstinence, male condom withspermicide, vasectomy should during study period and continue until 6 monthsafter the last dose of latest administered study drug

14. Patients must have completed all prior cancer treatments at least 2 weeks prior to 1st infusion of study drug including chemotherapy (includes also endocrinetreatment), radiotherapy, and major surgery.

• Prior anticancer biologic agent must have been completed at least 4 weeks priorto 1st infusion of study drug.

Exclusion Criteria:

1. Prior treatment with topoisomerase 1 inhibitors as a free form or as otherformulations.

2. Received any prior treatment with a Trop-2-directed ADC.

3. Patients with carcinomatous meningitis.

4. Known hypersensitivity reaction to any investigational or therapeutic compound ortheir incorporated substances.

5. Patients positive for HIV-1 or -2 with a history of Kaposi sarcoma and/orMulticentric Castleman Disease.

6. Have active hepatitis B virus (HBV) (defined as having a positive hepatitis Bsurface antigen test) or hepatitis C virus (HCV). In patients with a history of HBVor HCV, patients with detectable viral loads will be excluded.

7. Patients who test positive for hepatitis B surface antigen will be excluded.

8. Patients who test positive for hepatitis B core antibody will require HBV DNAby quantitative polymerase chain reaction (PCR) for confirmation of activedisease. Patients with positive hepatitis B core antibody but negative viralload by PCR may be eligible if they are being monitored for potential viralreactivation or are willing to start or maintain antiviral treatment duringstudy conduction (as dictated by their local and institutional standardpractice or guidelines). A patient with a history of HBV infection and presenceof hepatitis B surface antibody may participate in the study. In this lastscenario, viral load (HBV DNA) is not mandated.

9. Patients who test positive for HCV antibody will require HCV RNA byquantitative PCR for confirmation of active disease. Patients with a knownhistory of HCV or a positive HCV antibody test will not require an HCV antibodyat screening and will only require HCV RNA by quantitative PCR for confirmationof active disease.

10. Scheduled surgery during the study, other than minor surgery which would not delaystudy drug (eg, port insertion, tooth extraction, any procedure that requires < 1-hour general anesthesia. Procedures performed under local or intravenous (IV)/monitored sedation that lasts < 2 hours are acceptable).

11. Have an active second malignancy. Note: Patients with a history of malignancy thathas been completely treated, with no evidence of active cancer for 3 years prior toenrollment, or patients with surgically cured tumors with low risk of recurrence (eg, nonmelanoma skin cancer, histologically confirmed complete excision carcinomain situ, or similar) are eligible.

12. Known history of clinically significant bleeding, intestinal obstruction, orgastrointestinal perforation within 6 months of study initiation.

13. Active or prior documented inflammatory bowel disease (i.e. Crohn's disease,ulcerative colitis, or a preexisting chronic condition resulting in baseline grade ≥1 diarrhea).

14. Infection requiring antibiotic use within 1 week of 1st infusion of study drug.

15. Other concurrent medical or psychiatric conditions that, in the Investigator'sopinion, may be likely to confound study interpretation or prevent completion ofstudy procedures and follow-up examinations.

16. Women who are pregnant or lactating.

17. Concomitant participation in other interventional clinical trial. Note: Patientsparticipating in observational studies are eligible.

18. Any medical condition that, in the investigator's or sponsor's opinion, poses anundue risk to the patient's participation in the study

19. Use of other investigational drugs (drugs not marketed for any indication) within 28days or 5 half-lives (whichever is longer) of first dose of study drug.